scripts/tst-elf-edit.py

   1 #!/usr/bin/python3
   2 # ELF editor for load align tests.
   3 # Copyright (C) 2022 Free Software Foundation, Inc.
   4 # Copyright The GNU Toolchain Authors.
   5 # This file is part of the GNU C Library.
   6 #
   7 # The GNU C Library is free software; you can redistribute it and/or
   8 # modify it under the terms of the GNU Lesser General Public
   9 # License as published by the Free Software Foundation; either
  10 # version 2.1 of the License, or (at your option) any later version.
  11 #
  12 # The GNU C Library is distributed in the hope that it will be useful,
  13 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 # Lesser General Public License for more details.
  16 #
  17 # You should have received a copy of the GNU Lesser General Public
  18 # License along with the GNU C Library; if not, see
  19 # <https://www.gnu.org/licenses/>.
  20
  21 import argparse
  22 import os
  23 import sys
  24 import struct
  25
  26 EI_NIDENT=16
  27
  28 EI_MAG0=0
  29 ELFMAG0=b'\x7f'
  30 EI_MAG1=1
  31 ELFMAG1=b'E'
  32 EI_MAG2=2
  33 ELFMAG2=b'L'
  34 EI_MAG3=3
  35 ELFMAG3=b'F'
  36
  37 EI_CLASS=4
  38 ELFCLASSNONE=b'0'
  39 ELFCLASS32=b'\x01'
  40 ELFCLASS64=b'\x02'
  41
  42 EI_DATA=5
  43 ELFDATA2LSB=b'\x01'
  44 ELFDATA2MSB=b'\x02'
  45
  46 ET_EXEC=2
  47 ET_DYN=3
  48
  49 PT_LOAD=1
  50 PT_TLS=7
  51
  52 def elf_types_fmts(e_ident):
  53     endian = '<' if e_ident[EI_DATA] == ELFDATA2LSB else '>'
  54     addr = 'I' if e_ident[EI_CLASS] == ELFCLASS32 else 'Q'
  55     off = 'I' if e_ident[EI_CLASS] == ELFCLASS32 else 'Q'
  56     return (endian, addr, off)
  57
  58 class Elf_Ehdr:
  59     def __init__(self, e_ident):
  60         endian, addr, off = elf_types_fmts(e_ident)
  61         self.fmt = '{0}HHI{1}{2}{2}IHHHHHH'.format(endian, addr, off)
  62         self.len = struct.calcsize(self.fmt)
  63
  64     def read(self, f):
  65         buf = f.read(self.len)
  66         if not buf:
  67             error('{}: header too small'.format(f.name))
  68         data = struct.unpack(self.fmt, buf)
  69         self.e_type = data[0]
  70         self.e_machine = data[1]
  71         self.e_version = data[2]
  72         self.e_entry = data[3]
  73         self.e_phoff = data[4]
  74         self.e_shoff = data[5]
  75         self.e_flags = data[6]
  76         self.e_ehsize = data[7]
  77         self.e_phentsize= data[8]
  78         self.e_phnum = data[9]
  79         self.e_shstrndx = data[10]
  80
  81
  82 class Elf_Phdr:
  83     def __init__(self, e_ident):
  84         endian, addr, off = elf_types_fmts(e_ident)
  85         self.ei_class = e_ident[EI_CLASS]
  86         if self.ei_class == ELFCLASS32:
  87             self.fmt = '{0}I{2}{1}{1}IIII'.format(endian, addr, off)
  88         else:
  89             self.fmt = '{0}II{2}{1}{1}QQQ'.format(endian, addr, off)
  90         self.len = struct.calcsize(self.fmt)
  91
  92     def read(self, f):
  93         buf = f.read(self.len)
  94         if len(buf) < self.len:
  95             error('{}: program header too small'.format(f.name))
  96         data = struct.unpack(self.fmt, buf)
  97         if self.ei_class == ELFCLASS32:
  98             self.p_type = data[0]
  99             self.p_offset = data[1]
 100             self.p_vaddr = data[2]
 101             self.p_paddr = data[3]
 102             self.p_filesz = data[4]
 103             self.p_memsz = data[5]
 104             self.p_flags = data[6]
 105             self.p_align = data[7]
 106         else:
 107             self.p_type = data[0]
 108             self.p_flags = data[1]
 109             self.p_offset = data[2]
 110             self.p_vaddr = data[3]
 111             self.p_paddr = data[4]
 112             self.p_filesz = data[5]
 113             self.p_memsz = data[6]
 114             self.p_align = data[7]
 115
 116     def write(self, f):
 117         if self.ei_class == ELFCLASS32:
 118             data = struct.pack(self.fmt,
 119                                self.p_type,
 120                                self.p_offset,
 121                                self.p_vaddr,
 122                                self.p_paddr,
 123                                self.p_filesz,
 124                                self.p_memsz,
 125                                self.p_flags,
 126                                self.p_align)
 127         else:
 128             data = struct.pack(self.fmt,
 129                                self.p_type,
 130                                self.p_flags,
 131                                self.p_offset,
 132                                self.p_vaddr,
 133                                self.p_paddr,
 134                                self.p_filesz,
 135                                self.p_memsz,
 136                                self.p_align)
 137         f.write(data)
 138
 139
 140 def error(msg):
 141     print(msg, file=sys.stderr)
 142     sys.exit(1)
 143
 144
 145 def elf_edit_align(phdr, align):
 146     if align == 'half':
 147         phdr.p_align = phdr.p_align >> 1
 148     else:
 149         phdr.p_align = int(align)
 150
 151 def elf_edit_maximize_tls_size(phdr, elfclass):
 152     if elfclass == ELFCLASS32:
 153         # It is possible that the kernel can allocate half of the
 154         # address space, so use something larger.
 155         phdr.p_memsz = 0xfff00000
 156     else:
 157         phdr.p_memsz = 1 << 63
 158
 159 def elf_edit(f, opts):
 160     ei_nident_fmt = 'c' * EI_NIDENT
 161     ei_nident_len = struct.calcsize(ei_nident_fmt)
 162
 163     data = f.read(ei_nident_len)
 164     if len(data) < ei_nident_len:
 165       error('{}: e_nident too small'.format(f.name))
 166     e_ident = struct.unpack(ei_nident_fmt, data)
 167
 168     if e_ident[EI_MAG0] != ELFMAG0 \
 169        or e_ident[EI_MAG1] != ELFMAG1 \
 170        or e_ident[EI_MAG2] != ELFMAG2 \
 171        or e_ident[EI_MAG3] != ELFMAG3:
 172       error('{}: bad ELF header'.format(f.name))
 173
 174     if e_ident[EI_CLASS] != ELFCLASS32 \
 175        and e_ident[EI_CLASS] != ELFCLASS64:
 176       error('{}: unsupported ELF class: {}'.format(f.name, e_ident[EI_CLASS]))
 177
 178     if e_ident[EI_DATA] != ELFDATA2LSB \
 179        and e_ident[EI_DATA] != ELFDATA2MSB: \
 180       error('{}: unsupported ELF data: {}'.format(f.name, e_ident[EI_DATA]))
 181
 182     ehdr = Elf_Ehdr(e_ident)
 183     ehdr.read(f)
 184     if ehdr.e_type not in (ET_EXEC, ET_DYN):
 185        error('{}: not an executable or shared library'.format(f.name))
 186
 187     phdr = Elf_Phdr(e_ident)
 188     maximize_tls_size_done = False
 189     for i in range(0, ehdr.e_phnum):
 190         f.seek(ehdr.e_phoff + i * phdr.len)
 191         phdr.read(f)
 192         if phdr.p_type == PT_LOAD and opts.align is not None:
 193             elf_edit_align(phdr, opts.align)
 194             f.seek(ehdr.e_phoff + i * phdr.len)
 195             phdr.write(f)
 196             break
 197         if phdr.p_type == PT_TLS and opts.maximize_tls_size:
 198             elf_edit_maximize_tls_size(phdr, e_ident[EI_CLASS])
 199             f.seek(ehdr.e_phoff + i * phdr.len)
 200             phdr.write(f)
 201             maximize_tls_size_done = True
 202             break
 203
 204     if opts.maximize_tls_size and not maximize_tls_size_done:
 205         error('{}: TLS maximum size was not updated'.format(f.name))
 206
 207 def get_parser():
 208     parser = argparse.ArgumentParser(description=__doc__)
 209     parser.add_argument('-a', dest='align',
 210                         help='How to set the LOAD alignment')
 211     parser.add_argument('--maximize-tls-size', action='store_true',
 212                         help='Set maximum PT_TLS size')
 213     parser.add_argument('output',
 214                         help='ELF file to edit')
 215     return parser
 216
 217
 218 def main(argv):
 219     parser = get_parser()
 220     opts = parser.parse_args(argv)
 221     with open(opts.output, 'r+b') as fout:
 222        elf_edit(fout, opts)
 223
 224
 225 if __name__ == '__main__':
 226     main(sys.argv[1:])